Airship form



H. H. SUPLEE. AIRSHIP FORM.

APPLICATION FILED MAYZB, I921 "Patented Apr. 11, 1922.

UNITED STATES PATENT orrics.

HlNRY HARRISON SUPLEE, OF NEW YORK, N. Y.

AIRSI-IIP FORM,

Application filed May 28,

To all 207mm it may concern:

Be it known that I, HENRY HAmusoN SUP- Lnn, residing at New York city, in .the county of New York and State of New York, a citizen ot'the United States, have invented certain new and useful Improvements in Airship Forms; and I do hereby declare th following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it pertains to make and use the same.

My invention relates to airships of the type known as lighter than air 'airships,.and especially to that type known as rigid airships, in which the external form of the carene or hull may be given a form in accordance with definite calculations.

Experience has demonstrated that when the carene or hull of an airship is given such a formthat it offers a minimum aero dynamic resistance the following advantages are attained: the power required to propel the ship through the air at a given speed becomes a minimum; or, the speed attained for given power becomesanmximum; the radius of action for a given fuel-supply becomes amaximum; and the stresses upon the airship and mooring-mast or tower.

when the ship is moored in the open. be-

comes a minimum.

My invention consists in means for determining the form and proportions of the hull or carene oflan airship which shall attain the before-mentioned objects, and in the combination of the form and proportions of parts into a complete whole which shall have a minimum aerodynamic resistance under the conditions which may reasonably be en,- countered in practice.

The general form of an uirship'hull is that of a surface of rotation, being a spindleshaped body, intended to be propelled through the air in the general direction of its axis. The lift, or supportingpower of such an airship is due to the buoyancy of the gas, lighter than aiig with which it is filled, and hence the magnitui'le of this lift depends uprm the volume of the body or hull, The problem, therefore, requires that the determination of the best form of min imuin resistance include a constantvolume, otherwise the. lift, or capacity, and consequently the size of the ship would become a variable; The requirements, therefore, are that the volume, and the velocity of the ship remain constant, and that the ratio of max- Speciflcation of Letters Patent.

Patented Apr. 11, 1922.

1921. Serial No. 473,503.

in'lum diameter to length, as well as the profile curve, which, revolved about its axis, gives the form, be varied according to a predetermined method.

In deriving means for determining" the best form for anairship hull, I divide the total aerodynamic resistance into three parts; the head resistance; the surface fri tion; and the tail suction.

The head resistance opposed by the air to the entrance of the ship in its forward progress, corresponds practically to a uniformly distributed pressure, upon the pro- ]ected maximum cross-sectional area of the airship hull, and may be accurately determined for any given velocity in terms of said maximum crosssectional area.

The surface friction, due to the viscosity of the air, as it drags upon the hull of the ship during its forward motion, may be determined, for any given velocity, in terms of that portion of the surface of the hull of the ship upon which the air is pressed. andagainst which it rubs.

The tail suctionydue to theinertia of the air. and consequent laps of time dining which the air closes, in and fills the space from which the ship has moved in its for ward progress, is constant for any given speed, and is approximately measured by the difference between the head resistance and the friction of the hull for any given speed.

It follows that if the form of the hull be so shaped that the tail suction heeliminated and the head resistance and skin friction made equal to each'other and their difference consequently zero, the total resistance will.

become a minimum.

Theoretically the form which places the forces of a uniformly (listrilnited load in equilibrium is that commonly known the catenary; that is, the curve assumed by a chain of ui'liform weight per unit of length when suspended from two points upon a.

horizontal line or by a flexible cord, thread or other flexible means, to which uniform weights are suspended at equal intervals.

This, then, is the form which, when revolved about the axis,-gives a surface of rotation, forming the shape for the forward part of an airship hull which renders the head resistance a minimum. 7 I

If the forces which act to drag upon the rearward portion of the hull were uniformly distributed, this portion would also best be sence of normal surface pressure.

made in the form of a common catcnary. The forces acting upon the rearward portion, are, however, as has alrea(.y been stated, of two kinds; the skin friction, which is practically uniformly distributed, and the suction, which is not uniformly distributed, but is concentrated at the tail. The most efficient form of the rearward portion of an airship hull, according to my invention, is derived from a transformed catenary, ob; tained by, suspending a chain or uniformly loadedcord or other flexible means from two points on a horizontal line, and adding; thereto a tail loading, in theform of an additional weight, spring. tension. or similar force, proportional to the tail suction on the same scale asthe uniformly distributed forces.

This transformed catenary will then correspond to the profile of a shape in which the rearward drag of the slain friction, represented by the uniformly distributed forces. and the suction drag. represented by the additional force exerted uponthe tail, combine to produce the corresponding equi librium curve. A surface of revolution, formed by revolving such a transformed catenary upon its axis. will have its tail drawn out to fill the space in which the partial vacuum would otherwise be formed, and the drag of the suction will be practically eliminated.

The proportion of the whole airship hull which comes under the designation of the forward portion, to that which is termed the rearward portion, varies somewhat with the velocity of the ship through the air. Experiments under various velocities show, however, that for a distance of about fourtenths of the entire length. from the front end of the hull, the surface of the ship is subjected almost entirely to direct air resistance, and that on this portion of the hull there is either no lateral surface pressure. or

even a slight negative lateral pressure. For this portion of the hull, therefore, there is little or no skin friction, because ofthe ab- Eor the remaining six-tenths of the length of the hull there is a nearly uniform. normal pres sure. this acting" to produce a practically imiform frictional drag over this rearward portion of the hull. V

The ratio of maximum diameter to total. length of the hull varies somewhataccord ing to the rate of speed at which the ship is intended be operated, since the head resistance varies as the square of the velocity, and the. frictional resistance varies as a'somewhat lower power. according to the character of the surface of the hull;

I have found that the-most ellicicnt form of hull is that in which the head resistance and the frictional resistance are approximately equal to each other. If,therefore,

of pressure upon the hull.

the maximum cross section be increased, the head resistance will also be increased, while if the length of the hull be increased, the frictional resistance will be increased. I

have found that for very smooth surfaces the length of hull which will make the frictional resistance approximately equal to the head resistance is that in which the total length is about nine and one-half times the maximum diameter; while for surfaces which are less smooth the length which give a frictional resistance equal to the head resistance may be only about seven and onehalf times the maximum diameter; broadly, therefore I proportion the ratio of length to diameter such that the head resistance and frictional resistance are approximately equal to each. other to suit the particular conditions which arise in each case.

in general, the conditions which lead to the determination of the most efficientform for an airship hull moving through the air with least resistance maybe understood by imagining the hull to be composed of some gelatinous or soft material which could adapt itself in form to the influence of the forces acting upon it. It will be evident that such a material would have a tendency to be drawn out to a tapering form in the rear by the drag of the viscous air pressed against it. and pulled out at the tail by the suction at that point giving an additional. drag. and that these influences are precisely imitated by the transformed catenary as described above. It is also evident that the absence of any disturbingforces at that por tion of the hull where the negative pressures are being" reversed into positive pressures. would produce no effect-on any such supposed soft or gelatinous body, so that the location of the maximum cross section would be determined by the place of-such reve al The for 1d portion, having upon it pressures parallel to the axis of the ship would maintain the form ofequilibrium corresponding to that of a chain or other flexible member under vertical loads. which is the common catenary, so that from such general conditions it is evident that the combination of common and.

transformed catenaries. as in my invention, gives the outline of the form of'minimum resistance.

The objects of my'invention are attained by the means shown in the accompanying drawing". in which similar reference characters refer to the same parts in t e several figures.

Fig. 1. shows the general form of an airship hull according to my. invention, the ship being supposedto beproceedingg hrouc'h. the air in the direction indicated. by the arrowat l. Fi 2. shows a similar form of airship hull, exposed tothe forces produced by the flow of air proceeding in the direc:

tion of the arrows'at 1, or by the corresponding reactions when the airship is moving in the direction shown by the arrow in Fig. 1. Fig. 3, shows a transformed cate nary with tail loading, for the determination of the form of the rearward portion of the hull. Fig. h, shows the common catenary, as used for the determination of the form of the forward portion of the hull. Fig. 5, shows a catenary similar to that shown in Fig. 3, and for the same purpose, using a thread or cord, instead of a chain, with uniform weights suspended at equal intervals, and a spring tension for the tail loading, instead of the weight shown in Fig. Fig. 6, shows a. catenary for the determination of the form of the forward .portion of the hull, using a thread or cord,

with uniform weights suspended at equal intervals, instead of the chain shown in Fig. -il.

In Fig. 2, the small arrows show the gen eral distributionof pressuresupon an airship hull. determined in the wind tunnel. The direct pressures upon the front portion of the hull act in a line parallel to the axis of the hull as indicated by the arrows 8+8, until about one-third to four-tenths of the length of the ship has been passed. At or about this portion of the hull, the pressures upon the hull become nearly Zero, or are even slightly'negative, as indicated by the arrows 99 turning outward, this region of zero pressure being about fourtenths of the length of the hull from the forward end 1. At the point 5, on the axis of the ship, is shown the maximum diameter of the hull. the hull tapering aft nearly to a point, as shown at 2. r

The small arrows 10'10 shown in Fig. 2, from 2 to and from 2 to 4:, indicate that the air closing in upon the hull, exerts a nearly uniform pressure upon the surface, causing the frictional resistance upon this portion of the hull to be practically proportional to the area of the surface. At 2, the stream of air, closing in behind the tail at the rear end of the hull tends to form a partial vacuum, causing a suction of drag upon the tail. If the tail of the hull. is made blunt, the space in which this vacuum is formed. extends behind the airship in its progress, but if the tail of the airship is drawn out into the form assumed by this vacuum space, the greater part of this suction is prevented, and the resistance to the forward movement of the airship is thereby diminished.

In order to determine the correct profile curves to provide a shape of minimum re sistance, I proceed as follows: Taking the maximum diameter of the hull, 34, laid off upon ahorizontal line, as in Fig. at, and drawing the axis 1-5 in a vertical position, as shown, I suspend a flexible chain 11, as

of uniform'weight per unit of length assumes the form of the common catenary; in Fig. 6, the thread or cord 12, has suspended from its uniform weights 13 at equally spaced intervals, this arrangement giving a curve of similar form to that given by the chain 1 of Fig. 4. The catenary curve thus obtained is the equilibrium form for uniformly distributed equal forces, and gives directly the profile of minimum resistance for the forward portion of the ship.

For the determination of the form of min imum resistance for the rearward portion of the airship, I suspend a similar chain 14;

from the extremities of a horizontal line 3-4 Fig. 3, the distance being equal to the maximum diameter of the hull of the ship. The common catenary which such a chain would assume would give the equilibrium curve for the uniformly distributed frictional forces. I then suspend to the bot tom of this chain, at 2, Fig. 3, the weight 6. thisweightbeing equal in magnitude to the suction force acting upon the tail. of the airship when in motion. This .weight 6, transforms the catenary of Fig. 3, into the pointed shape, as shown, the pointed, tapering tail filling out the space which would otherwise correspond to the suction vacuum behind the ship, preventing the eddying re actionswhich would otherwise be formed. and causing the air to pass off behind the ship in smooth stream lines. By using the curve thus obtained in Fig. 8 for the rearward portion of the ship, and the curve obtained in Fig. 4:,for the forward portion of the ship. the form shown in Fig. 1, is obtained, giving the minimum resistance to the passage through the air. Fig. 5, shows the use of a thread or cord 15, with uniform weights l6, suspended at equal intervals, in stead of a chain for the. determination of the catenary curve, and also shows the use of a spring 7, instead of a weight 6, for the additional loading at the tail, correspoinling to the tail suction.

The magnitude of the load to be added t the bottom of the catenary, as shown in Fig. 3 or Fig. 5, to correspond to the tail. suction may be obtained by measurement in the wind tunnel, or it may be obtained with approximate accuracy by making it equal in weight to that of a length of the chain equal to the difference between the lengths of. chain for the determination of the forward portion and that for the rearward portion of the airship hull.

Experience has shown that the total resistance to the n'ogress of the ship through the air is a minnnum when the resistance of the t vo portions of the ship are equal to each other. This equality of resistance occurs when the ratio of length 1-2 is from seven and one-half to nine and onehalf times the maximum diameter 3 the greater ratio existing when the sin-lace of the airship is.

very smooth, and the ratio diminishing when the surface of the airship is rougher. or when the frictional resistance is materially increased by reason of irregularities in form or protuherances upon the ship.

I do not wish to be understood as limiting myself to the specific details of construction and arrangement as herein described and illustrated, as it is manifest that variations and modifications may he made in the features of construction and arrangement in the adaptations of the method to various conditions of use without departing from the spirit and scope of my invention and improvements. 1. therefore reserve the right to all such variations and modificatlons as properly fall within the scope of my invention, and the terms of the follow curve proportional to the suction force acting upon the tail of the airship when in motion.

3. An airship form comprising a portion consisting of a transformed catenarian surface of revolution derived from rotating a transformed catenarian curve upon its major axis and means for causing the trans.

loadupon formation of said surface by applying ings n'oportional to the forces acting the airship when it is in motion.

el. A form for airships having a rearward portion comprising a surface of revolution derived from rotating a transformed catenarian curve upon its major axis and means for transforming said portion by applying to the sides a vertical tension proportional to the surface frictional forces acting during motion, and simultaneously applying to the lowermost point of the curve a vertical tension proportional to the suction force acting upon the tail when the airship is in motion.

5. In an air ship form the ends ofwhich have catenarian surfaces of revolution about major axes, means for producing the same comprising a chain and tension applied to the lower portion thereof for the purpose of causing the shape of said chain to be transformed toa degree proportional to the suction force acting upon the tail of the airship when in motion.

6. In an airship form the ends of which have catenarian surfaces of revolution about major axes, means for producing the same comprising a chain or other flexible means, loadings applied at intervals to said chain the weights of which are proportional to the forces acting upon the profile curve when the ship is in motion.

7. The method of determining a profile curve for an airship consisting in suspending a chain or other flexible means from the extremities of a horizontal line equal in length to the maximum diameter of said airship. applying to said chain or flexible means tensions proportional to the aerodynamical forces acting upon said airship when in motion through the air, or when stationary in a wind tunnel or chamber and rotating said chain or means'upon its major In testimony whereof I have affixed my signature.

HENRY nannisonsuimun 

